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It's really a lot simpler than what you'd think. The reason that we benefit so much from indexed plugs, is because our spark plugs are threaded offset into the combustion chamber. Because of this, if the plug is faced wrong, the spark will be going up into the roof of the combustion chamber, instead instead of down in the air/fuel mixture. Indexing wouldn't be necessary in a dohc head with a plug going straight down into the combustion chamber.

The Harley's have their plugs indexed toward the intake valve because otherwise would be open toward the wall of the combustion chamber, It wouldn't matter to much if it was open toward the exhaust. In our engine though, since we're a 4 valve sohc, it's important that we have our plugs indexed toward the exhaust valves / firewall so the open side will aim down into the combustion chamber. Here's a quick read about plug indexing:

Re: NITRO can correct me if I'm wrong...

Notice how he says that indexing the plugs on a d16a6 can make anywhere from 4-8hp, (on a 108hp engine). He recommends the d16a6 have the ground electrode aim toward the exhaust (open side face intake valves). This engine spins in the opposite direction as ours, putting the intake valves on the firewall side. The spark plugs are also on the same side as our cars.
And, as I wrote earlier, you will never be able to tell which way they point,
unless you index them yourself, or watch as someone else does... The
operation of the car will not change in any perceptible way..
Racing, with high-strung engines running nitro is a whole different animal.

And, yes, I did index mine - just because. I used indexing washers.
 

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And, as I wrote earlier, you will never be able to tell which way they point,
unless you index them yourself, or watch as someone else does... The
operation of the car will not change in any perceptible way..
Racing, with high-strung engines running nitro is a whole different animal.

And, yes, I did index mine - just because. I used indexing washers.
Just trying to explain the mechanics behind indexing since I didn't read any definite answer in this thread as to which way the open side of the plug should be facing. It might not make a big difference in power, but hopefully it will be slightly noticeable in mpg. I'll soon find out, just picked up a set of Moroso indexing washers.
 

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I wish I had bothered to look before I leaped. So I am trying to get our Gen 1 back on the road. I have a laundry list of things the car needs so I started ordering parts and things needed to get the car on the road. Yesterday I was in the auto parts store just looking for some ramps so that we could work on the car. While I was there I thought I should go ahead and just get a set of plugs. Completely unaware there was anything special I needed to know about plugs.... I figured the guy at the counter looks up my make, model, and year and they tell me which plug I need. So that I what I did. The recommended plug was an Autolite Iridium plug. So I arrived back home, and my son was ready to work on the car so I handed off the parts, oil, filters etc needed and I went about running errands. So the plugs were changed yesterday. The original NGK's were still in the car it looked like. The plugs were pretty nasty looking and the car seems to be running really well with the new Autolites. However I knew nothing about this indexing requirement, or that there was anything special that needed to be done. So while looking for some more info on other things I stumbled across some spark plug threads including this one and now realize the error of our ways. So I just ordered a set of the Honda NGK plugs to match the index for our car. The NGK's that came out of the car were all the A index plugs so that is what I just ordered. I sure wish I had known this before we put those Autolites in the car. I will just use them until the NGK's show up along with the other parts we are waiting on.

Who knew something as simple of spark plugs would be such an adventure? Thanks for the info.

Longsnowsm
 

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I wish I had bothered to look before I leaped. So I am trying to get our Gen 1 back on the road. I have a laundry list of things the car needs so I started ordering parts and things needed to get the car on the road. Yesterday I was in the auto parts store just looking for some ramps so that we could work on the car. While I was there I thought I should go ahead and just get a set of plugs. Completely unaware there was anything special I needed to know about plugs.... I figured the guy at the counter looks up my make, model, and year and they tell me which plug I need. So that I what I did. The recommended plug was an Autolite Iridium plug. So I arrived back home, and my son was ready to work on the car so I handed off the parts, oil, filters etc needed and I went about running errands. So the plugs were changed yesterday. The original NGK's were still in the car it looked like. The plugs were pretty nasty looking and the car seems to be running really well with the new Autolites. However I knew nothing about this indexing requirement, or that there was anything special that needed to be done. So while looking for some more info on other things I stumbled across some spark plug threads including this one and now realize the error of our ways. So I just ordered a set of the Honda NGK plugs to match the index for our car. The NGK's that came out of the car were all the A index plugs so that is what I just ordered. I sure wish I had known this before we put those Autolites in the car. I will just use them until the NGK's show up along with the other parts we are waiting on.

Who knew something as simple of spark plugs would be such an adventure? Thanks for the info.

Longsnowsm
You just wasted your money; there's no detectable difference by any
reference as to whether or not plugs are indexed. But, I did mine with
indexing washers "just because..."
 

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So the manufacturer specified 4 different plug part numbers, but it really doesn't matter? I am trying to make sure I understand. Normally I wouldn't expect Honda or a company to specify 4 different parts if it didn't matter. Any ideas why that would be the case?

InsightCentral.net - Encyclopedia - Honda Insight Iridium Spark Plugs

I just wish I had known about any of this before I ran off and bought plugs.

Longsnowsm
 

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So the manufacturer specified 4 different plug part numbers, but it really doesn't matter? I am trying to make sure I understand. Normally I wouldn't expect Honda or a company to specify 4 different parts if it didn't matter. Any ideas why that would be the case?

InsightCentral.net - Encyclopedia - Honda Insight Iridium Spark Plugs

I just wish I had known about any of this before I ran off and bought plugs.

Longsnowsm
Plug indexing has long been used in very high compression engines as a
"tweak"..especially in drag racing. But, if you ask the racers, they'll say they
notice no difference, but do it "just in case it might help".

Honda did everything they could think of to make a decent
running very efficient car in the Insight. The plug thing is a tiny, tiny tweak
that "may" have positive benefit, but so slight as to not likely be measurable.

The only way you'll know your plugs are, or aren't indexed is if you look....

Now, the iridium part is a different matter, as they last many times longer
than regular plugs. Replacement is not required till 105K; pretty long time
for plugs.
 

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Plug indexing has long been used in very high compression engines as a
"tweak"..especially in drag racing. But, if you ask the racers, they'll say they
notice no difference, but do it "just in case it might help".

Honda did everything they could think of to make a decent
running very efficient car in the Insight. The plug thing is a tiny, tiny tweak
that "may" have positive benefit, but so slight as to not likely be measurable.
We really don't know how much of a difference Honda-indexed plugs make until someone who can get high mpg's (say 100mpg) out of an Insight-I actually does a controlled mpg comparison test with Honda-indexed vs plugs 90, 180, and 270 degrees out of index. I bet Honda tested this before they went to the extra expense (to them) of 4 part numbers vs 1.

I'm saying "Honda-indexed" because per previous discussion in this thread we don't know how Honda specs the orientation of the plugs. Folks using indexing washers appear to assume that the plug gap should face between the two intake valves, but this is an atypical engine and that may not be the case given its reliance (especially in lean burn) on swirl.

I'll stick with the Honda-indexed plugs. Experience from racing isn't necessarily relevant to the Insight, especially for MT's in lean burn (which race engines don't do!). Racing aims for HP, which isn't the same thing as mpg. Factoring in the 105k change interval and the convenience of not having to mess with indexing washers, the extra expense of the Honda plugs doesn't bother me.
 

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Saying that indexing the plugs isn't necessary is just plain silly. I understand the theories behind both scenarios, but there is no way that Honda would have bothered to have four different indexed plugs made and go through the trouble of identifying and stamping the head with the correct plug letter if it did not matter.

If you look at a picture of the combustion chamber side of the head with the plugs installed, you will see that correctly indexed plugs point directly towards the non-VTEC intake valve. That is, the open end of the ground electrode points to the center line of the valve.

Realize that when the car is in lean burn mode, you are producing exactly enough power to maintain speed. Nothing more, nothing less. Considering the overall low drag of our cars, I would be willing to bet the car is only producing about 8HP @ 1800RPM @ 55MPH @ a 24:1 AFR. It could even be less.

Comparing our engines to a drag engine is just plain ludicrous. When you realize what lean burn is accomplishing, we must ensure that every last molecule of fuel is burned. If plug indexing is going to help with that, it is a worthwhile endevour. With the above in mind, if plug indexing even gives us a 0.25HP boost, that is 3.125% of 8HP. That is not insignificant when you're dealing with HP numbers in the single digits to lower teens.
 

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I'll stick with the Honda-indexed plugs. Experience from racing isn't necessarily relevant to the Insight, especially for MT's in lean burn (which race engines don't do!). Racing aims for HP, which isn't the same thing as mpg. Factoring in the 105k change interval and the convenience of not having to mess with indexing washers, the extra expense of the Honda plugs doesn't bother me.
HP and efficiency go hand in hand. Remember, plug indexing was discovered in racing. It makes more HP because it allows you to burn your a/f mixture effectively. Which is why it also makes the motor run more efficiently and thus, higher mpg. The plugs grounding electrode should be on the intake side, open end of the plug aiming at the exhaust, NOT the intake valve (if you aim the open end toward the intake, your spark is directed into the roof of the combustion chamber, VTEC and swirl don't matter, plug indexing works the same no matter if its a v8 or moped). My OEM plugs were aiming slightly toward the intake valve, now I have the plug electrode centered between the intake valves, open side facing between the exhaust. After I did this, i'm now able to cruise at 40 mph (no wind) at 100-125mpg which I was never able to do before with the OEM plugs.

Just running OEM plugs and not checking how they actually align compared to how they should be aligned is blind faith.
 

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HP and efficiency go hand in hand. Remember, plug indexing was discovered in racing. It makes more HP because it allows you to burn your a/f mixture effectively. Which is why it also makes the motor run more efficiently and thus, higher mpg. The plugs grounding electrode should be on the intake side, open end of the plug aiming at the exhaust, NOT the intake valve (if you aim the open end toward the intake, your spark is directed into the roof of the combustion chamber, VTEC and swirl don't matter, plug indexing works the same no matter if its a v8 or moped). My OEM plugs were aiming slightly toward the intake valve, now I have the plug electrode centered between the intake valves, open side facing between the exhaust. After I did this, i'm now able to cruise at 40 mph (no wind) at 100-125mpg which I was never able to do before with the OEM plugs.

Just running OEM plugs and not checking how they actually align compared to how they should be aligned is blind faith.
The pictures of the head I have seen off the car, looking at the combustion chamber side, have all three ground electrodes pointing directly at an intake valve; presumably the non-VTEC one.

It actually looks pretty neat, to see them all exactly the same. Usually they're all over the place on a regular car's head. Let me see if I can find anything...

Edit: eBay to the rescue! Look through the pictures, and it clearly shows what I mean.

http://cgi.ebay.com/ebaymotors/2000...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

I admit that it's possible this person has three of the wrong plugs installed.... but that is what I remember seeing before.
 

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The pictures of the head I have seen off the car, looking at the combustion chamber side, have all three ground electrodes pointing directly at an intake valve; presumably the non-VTEC one.

It actually looks pretty neat, to see them all exactly the same. Usually they're all over the place on a regular car. Let me see if I can find anything...

Edit: eBay to the rescue! Look through the pictures, and it clearly shows what I mean.

2000 - 2006 Honda Insight Hybrid Engine Cylinder Head - eBay (item 280629900436 end time Mar-15-11 16:32:44 PDT)

That's not how it should be for best results. The open end of the plug should be aimed at the camera so the spark energy is directed to the un shroded area of the combustion chamber. Like that the spark energy is directed up and not down toward the piston.

Read some explanations like the link I posted on page previously to see the idea behind spark plug indexing. It's not done in a unique way for the insight The idea is the same no matter what the application.

My plugs were aimed the way you're saying and I saw a notable increase in mpg when I indexed them properly.
 

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Right so ground electrode on the intake valve side, open end aiming at the exhaust valve (down toward the piston). Right?
No. The open end points towards an intake valve. Like I said, this is what I remember seeing before.. but it is possible that this person has three of the wrong plugs installed? LOL.

I guess I could ask him if the plugs in it match the stamping on the heads.
 

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There isn't going to be a "right" for every engine. It will depend entirely on combustion chamber design, flow patterns, etc, etc. We're really just guessing when we make up possible reasons for the motive(s) behind Honda's engineering.

If the goal is to find out the indexing as Honda intended it, that is what I intend to do.
 

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Yes there is... The point of spark plug indexing is to expose the spark energy to the largest area of the combustion chamber. No matter what engine you do it to, the idea is always the same, aim the spark into fuel and air, not into metal.
 

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HP and efficiency go hand in hand. Remember, plug indexing was discovered in racing. It makes more HP because it allows you to burn your a/f mixture effectively. Which is why it also makes the motor run more efficiently and thus, higher mpg.
Well, no. If you don't need that additional top-end HP, then this "efficiency" gains you nothing. Performance people often confuse "HP efficiency" with mpg efficiency. They're not the same. If I need 8HP to cruise, I want to generate that 8HP with as little gas as possible. Tuning an engine to generate 110HP from the same amount of gas that it originally needed to make 100HP may not translate into savings when it is producing just 8HP. Performance tuning is not the same as tuning an engine for mpg.
After I did this, i'm now able to cruise at 40 mph (no wind) at 100-125mpg which I was never able to do before with the OEM plugs.
Mine cruises quite nicely at 45-50mph at 100mpg (summer gas and reasonable temps) and the OEM plugs haven't been touched (I bought the car new).
VTEC and swirl don't matter, plug indexing works the same no matter if its a v8 or moped).
Actually, no. Lean burn is a special situation. For LB, the charge is intentionally unevenly distributed in the combustion chamber in such a way that richer mixture surrounds the spark. Ignition begins a burn in this richer zone that then spreads to leaner parts of the mixture, avoiding detonation. Remember that if the overall mixture is 24:1 and the richer zone is stoichiometric 14:1, the rest must be much leaner than 24:1 to average out at 24:1.

Originally Honda got lean burn via feeding in a richer mixture through a third intake valve close to the plug. Since Insight-I's have just 2 intake valves, Honda probably generates this asymmetry through some combination of
- opening the VTEC valve slightly to generate swirl and also possibly to lean out the mixture
- indexing the plug so the spark is in the richest part of the charge after compression (remember, ignition occurs AFTER the valves close and AFTER the piston moves up towards TDC, which gives a swirling mixture time to move)
Just running OEM plugs and not checking how they actually align compared to how they should be aligned is blind faith.
I'm with you there, partly. When I do swap plugs, I'll check the alignment of the original plugs and then make sure the replacement OEM plugs line up the same way. But it's also blind faith to decide how they "should" be aligned without any testing and without knowing what orientation Honda determined was best, probably after a lot of testing.
 

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And what is the replacement NGK plug for the original ILZFR5A11 and where to buy it besides the dealer at nearly $15 each?
 

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Well, no. If you don't need that additional top-end HP, then this "efficiency" gains you nothing. Performance people often confuse "HP efficiency" with mpg efficiency. They're not the same. If I need 8HP to cruise, I want to generate that 8HP with as little gas as possible. Tuning an engine to generate 110HP from the same amount of gas that it originally needed to make 100HP may not translate into savings when it is producing just 8HP. Performance tuning is not the same as tuning an engine for mpg.
It gains you more mpg. They are the same in the sense that when your engine runs more efficiently, it makes more power. There's lots of ways to do it. When you gain hp from your ignition system, you also gain mpg.

Mine cruises quite nicely at 45-50mph at 100mpg (summer gas and reasonable temps) and the OEM plugs haven't been touched (I bought the car new).
That's great, but mine didn't with OEM plugs marked for my engine. I put that there for comparison, not to in any way compete with anyone on this site.

Actually, no. Lean burn is a special situation. For LB, the charge is intentionally unevenly distributed in the combustion chamber in such a way that richer mixture surrounds the spark. Ignition begins a burn in this richer zone that then spreads to leaner parts of the mixture, avoiding detonation. Remember that if the overall mixture is 24:1 and the richer zone is stoichiometric 14:1, the rest must be much leaner than 24:1 to average out at 24:1.

Originally Honda got lean burn via feeding in a richer mixture through a third intake valve close to the plug. Since Insight-I's have just 2 intake valves, Honda probably generates this asymmetry through some combination of
- opening the VTEC valve slightly to generate swirl and also possibly to lean out the mixture
- indexing the plug so the spark is in the richest part of the charge after compression (remember, ignition occurs AFTER the valves close and AFTER the piston moves up towards TDC, which gives a swirling mixture time to move)
Air and fuel are sucked into the engine, compressed, and then ignited. Ignition goes off around TDC, all the air and fuel is there when the spark goes off regardless where the fuel likes to hang out. This is way simpler than you all make it out to be. You can see in that pic Eli linked that the spark plug is in a pocket between the exhaust valves, with the plugs aim up, it's completely shrouded, sideways the way it is in that pic isn't far off.

I'm with you there, partly. When I do swap plugs, I'll check the alignment of the original plugs and then make sure the replacement OEM plugs line up the same way. But it's also blind faith to decide how they "should" be aligned without any testing and without knowing what orientation Honda determined was best, probably after a lot of testing.
The OEM plugs have a black line on them on the silver hex part so you can do just that. Don't go by the letter on the top as they're not the same on each plug..

It's not blind faith deciding how they should be aligned. Read what the people that came up spark plug indexing have to say. There's a very simple reason why they do it.
 

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That's great, but mine didn't with OEM plugs marked for my engine. I put that there for comparison, not to in any way compete with anyone on this site.
Sorry, I was just trying to indicate that the factory orientation, whatever it is, works quite well.
Air and fuel are sucked into the engine, compressed, and then ignited. Ignition goes off around TDC, all the air and fuel is there when the spark goes off regardless where the fuel likes to hang out. This is way simpler than you all make it out to be. You can see in that pic Eli linked that the spark plug is in a pocket between the exhaust valves, with the plugs aim up, it's completely shrouded, sideways the way it is in that pic isn't far off.
I'm sorry I'm not explaining it adequately. Here's a Wiki article: Lean burn - Wikipedia, the free encyclopedia
The part on Honda says:
"This stratified-charge approach to lean-burn combustion means that the air-fuel ratio isn't equal throughout the cylinder. Instead, precise control over fuel injection and intake flow dynamics allows a greater concentration of fuel closer to the spark plug tip (richer), which is required for successful ignition and flame spread for complete combustion. The remainder of the cylinders' intake charge is progressively leaner with an overall average air:fuel ratio falling into the lean-burn category of up to 22:1.
The older Honda engines that used lean burn (not all did) accomplished this by having a parallel fuel and intake system that fed a pre-chamber the "ideal" ratio for initial combustion. This burning mixture was then opened to the main chamber where a much larger and leaner mix then ignited to provide sufficient power. During the time this design was in production this system (CVCC, Compound Vortex Controlled Combustion) primarily allowed lower emissions without the need for a catalytic converter. These were carbureted engines and the relative "imprecise" nature of such limited the MPG abilities of the concept that now under MPI (Multi-Port fuel Injection) allows for higher MPG too."
and
"This lean-burn ability by the necessity of the limits of physics, and the chemistry of combustion as it applies to a current gasoline engine must be limited to light load and lower RPM conditions."

It's not blind faith deciding how they should be aligned. Read what the people that came up spark plug indexing have to say. There's a very simple reason why they do it.
The people that discovered indexing were doing it for a different situation and purposes than Honda is doing it (stratified charge,lean burn, MPG). Therefore the optimum orientations may not be the same.
 
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